Squirrel,
There are no stupid questions - but remember this is a rumour 'blog' and actually just shooting the breeze here!
But to try and answer your question - and it really is the only reality pill that I personally swallow is that of fleet management and TLS.
Adding another aircraft type to the UK inventory will not do us any favours and when looking at commonality of training and spares alone adding Blackhawk or CH53 or NH90 or anyother worthy 'old' FMH potential suitor not only significantly adds cost, but also will take an awful amount of time to enter service.
Hence why although I do not think a Merlin/CH47 is not the turn key solution, but if Prime Minister Brown, HMT and civil serpents are serious about increasing rotary wing lift then there is every possibility that it will deliver a large increase in short time frames. Conceivably CHF aircrew could start green Merlin conversions tomorrow (aircrew and gingers) as could Merlin crews to CH47 - all with spares and TLS contracts in place for the initial stages of the transition.
And as to keeping a weather eye on future requirements, then as already discussed, CH47s are a huge lift capability, and will only get better with engine and avionic upgrades. Admittedly the Fisheads should also have had CH47, but given their current archaic aircraft, then Merlin is not that bad and I dare say that the Fisheads will make their deck cycles and the rest of their oggin gumpf work as well as potentially help the rest of JHC in land locked conflicts.
If Merlin to the Fisheads is the only political/UK industry compromise (to keep AW ticking over and not really admit (for export purposes) that it was an SH white elephant) then for the greater good of rapidly procuring 20 or so more CH47 will be worth it for the overall requirement, namely the boots on the ground.